To provide an internal combustion engine that is superior in fuel efficiency, emission level and other properties, values of engine control parameters (the fuel injection amount, the air fuel ratio, the time of ignition, the time of fuel injection, or the EGR rate, for example) have to be appropriately corrected in response to the property of the fuel. To achieve this, there are proposed various apparatuses for detecting the fuel property in order to optimally control the internal combustion engine in response to the fuel property.
To comply with the law that requires automobiles to have an on-board diagnosis (OBD) system, it may sometimes be required that it is possible to determine whether or not a fuel property detecting apparatus is normally operating and to immediately detect any abnormality occurring in the fuel property detecting apparatus.
Japanese Utility Model Laid-Open No. 2-112949 discloses a technique of outputting an alarm signal when the variation of the alcohol concentration of an alcohol blended fuel detected by an alcohol concentration sensor is equal to or higher than a predetermined value, and monitoring the variation of the air fuel ratio for a predetermined length of time if the alarm signal is output, and determining that there is an abnormality in the alcohol concentration sensor if a deviation of the air fuel ratio is detected.